Site-specific metal bonding to xanthine in the tripodal tris(2-aminoethyl)amine (tren) ligand-system: Crystal structures of [Zn(tren)(H2xan)] · ClO4 · H2O, [Cd(tren)(H2xan)] · ClO4 · H2O, [Ni(tren)(H2xan)(H2O)] · ClO4 · H2O, and [Cu2{(μ-Hxan)Cu(tren)}2(μ-

Bernhard Lippert has contributed significantly to the understanding of metallamacrocyclic complexes with low valent, late transition metals. In particular, he has pioneered the preparation of metallacalixarenes such as 12-MC-3 and 16-MC-4 structure types. In this article, we provide the preparation of a new 16-MC-4, [Mn4Br4(B(tBuM)PZG)4] [Mn(HOCO2)2], complex made with the ligand potassium N,N-bis(3-methyl-5-tert-butylpyrazolylmethyl)glycinate (KB(tBuM)PZG). In addition to being the first 16-MC-4 that is composed of manganese, this complex is the first example of a transition metal [Mn(II)] being captured in the interior cavity of the 16-MC-4. We discuss how our ligand design leads to the isolated structure due to the steric bulk that has been appended to the pyrazole ligand.